Studies on the Mechanisms for the Transport of Lithium Ions in Solid-State Composites Using a New Combination of Li NMR Methods

鉴于与能源和信息技术的高度相关性，最近大量的研究集中在固态电解质中的离子动力学上。尽管有这些努力，我们对固体中离子传输的理解仍然不完整，这限制了基于知识设计新材料的可能性。全面的实验表征奠定了基本理解的基础。在这里，我们建议利用固态核磁共振是研究固态电解质中离子复杂运动的有力工具。具体来说，我们打算使用宽谱的6Li和7Li核磁共振方法来确定锂离子在各种时间尺度和长度尺度上的动力学。在微观长度尺度上的动力学研究中，首次将刺激回波实验与场循环实验相结合。前者可以直接测量离子运动的相关函数，而后者可以通过确定自旋晶格弛豫时间T1的频率依赖性来获得离子运动的谱密度。这两种技术的时间窗以一种理想的方式相互补充，使我们能够覆盖大约0.1秒- 10秒的时间范围。为了研究锂离子在介观和宏观长度尺度上的输运，计划在静场梯度下通过核磁共振实验测量自扩散系数。将这种新的6Li和7Li核磁共振组合方法应用于锂离子在不同时间尺度和长度尺度上的运动，我们打算追溯到固体基质中的基本离子跳跃的远程传输和电导率。我们的研究将集中在复合材料上，复合材料在寻求具有改进材料性能的固态电解质方面引起了极大的关注。具体来说，我们建议研究复合材料，其中固体基体在不同的空间区域表现出不同的结构或成分。选择体系的一个重要标准是结构非均质性的增加伴随着离子电导率的增加。具体来说，值得研究的两个有趣的例子是（Li2S）_x(P2S5)_（1-x）玻璃陶瓷和（Li2S）_0.5-[(1-x)GeS2-xGeO2]_0.5混合网络前体玻璃。为了确定这些复合材料离子电导率增强的原因，将从结构的非均质性出发，确定离子传输的机制。这一知识将对将来改进固态电解质的电导率有很大的用处。

In view of a high relevance in energy and information technologies, a large number of recent research studies have focused on the dynamics of ions in solid-state electrolytes. Despite these efforts, our understanding of ion transport in solids is still incomplete, limiting the possibilities of a knowledge-based design of new materials. The foundations for a fundamental understanding are laid by a comprehensive experimental characterization. Here, we propose to exploit that solid-state nuclear magnetic resonance is a powerful tool to investigate complex motions of ions in solid-state electrolytes. Specifically, we intend to use a broad spectrum of 6Li and 7Li NMR methods to ascertain dynamics of lithium ions on a large variety of time scales and length scales. For a study of dynamics on microscopic length scales, stimulated-echo experiments and field-cycling experiments will be combined for the first time. The former enable a direct measurement of correlation functions of the ionic motion, while the latter provide access to the spectral density of the ionic motion via a determination of the frequency dependence of the spin-lattice relaxation time T1. The time windows of both these techniques complement each other in an ideal way, allowing us to cover a time range of ca. 1 ps - 10 s. To study the transport of lithium ions on mesoscopic and macroscopic length scales, it is planned to measure self-diffusion coefficients by means of NMR experiments in static field gradients. Applying this new combination of 6Li und 7Li NMR methods to the lithium ionic motion on various time scales and length scales, we intend to trace back long-range transport and conductivity to elementary ionic jumps in a solid matrix.Our studies will focus on composites, which have attracted a great deal of attention in the quest for solid-state electrolytes with improved material properties. Specifically, we propose to investigate composites where the solid matrix exhibits distinguishable structures or compositions in different spatial regions. An important criterion for the selection of the systems is that an increase of structural heterogeneity is accompanied by an increase of the ionic conductivity. In detail, two interesting examples to be studied are (Li2S)_x(P2S5)_(1-x) glass-ceramics and (Li2S)_0.5-[(1-x)GeS2-xGeO2]_0.5 mixed-network former glasses. In order to ascertain the origin of the enhanced ionic conductivity of these composite materials, the mechanism for the ion transport will be ascertained in the light of the structural heterogeneity. This knowledge will be of great use for a future improvement of the electric conductivity of solid-state electrolytes.